1. Field of the Invention
The present invention relates generally to a video signal recording apparatus and, more particularly, to a video signal recording apparatus of the type employing a plurality of rotary heads.
2. Description of the Related Art
It is known that video tape recorders of the rotary-head type have gained in popularity as a domestic electronic appliance. Such a rotary-head type of video tape recorder (hereinafter referred to simply as "VTR") is arranged to record or reproduce video signals while forming a series of oblique tracks on a recording medium, for example, a magnetic tape. In order to increase recording density, no guard band is provided between adjacent tracks, and crosstalk occurring between adjacent tracks during reproduction is therefore suppressed by utilizing azimuth loss which is provided by making the azimuth angle of recording and reproducing heads differ between the adjacent tracks.
In such a VTR, it is necessary that the reproducing head accurately trace each track formed on the magnetic tape, and tracking control for controlling the tracing operation plays an important role.
A video signal recording apparatus of the conventional type having the ability to perform high-density recording and reproduction, for example, a digital video recorder, generally employs what is called the area-division ATF (Automatic Tracking Finding) method for purposes of tracking control. This method is known as a representative tracking method in the field of digital aidio tape recorders (DAT). In accordance with such a method, each track is provided with a tracking controlling area independent of an area on which main video data is recorded, and a pilot signal is recorded in the tracking controlling area.
In this area-division ATF method, the number l of tracks corresponding to a repetitive recording pattern of pilot signals recorded on the magnetic tape, has been selected to be equal to the number m of tracks required to record a predetermined set of signals, for example, one frame of video signals.
Recording and reproduction for the case where m=l=6; n=4 (n: the number of heads) are explained below with illustrative reference to FIG. 1. FIG. 1 is a diagram showing a recording pattern formed on a magnetic tape, and a series of recording tracks 2 are shown as being formed on a magnetic tape 1 which serves as a recording medium. As illustrated, since the period of each recording pattern of ATF pilot signals corresponds to the number of tracks required to record one frame of video signals, the recording pattern shown in FIG. 1 is obtained. In the figure, "Data" represents a video signal, and ATF1 to ATF6 represent a series of ATF pilot signals for one period. If tracking is performed on a tape transport system in order to reproduce such a recording pattern, it follows that servo introducing points exist for each period of the recording pattern consisting of a series of ATF pilot signals. In this case, because of m=l=6, a servo introducing point appears every six tracks. In other words, in the conventional arrangement which relies on m=l, the number of tracks required to record one frame of video signals means the number of servo introducing points in a tape transport servo system.
However, if a particular kind of video signal which contains a large amount of information, such as a high-definition television signal, is to be recorded, the number of tracks required to record video signals for one frame increases, with the result that it will take a long time until the tape transport servo system introduces its servo control. Moreover, in a case where it is assumed that the series of recording tracks 2 of FIG. 1 is subjected to recording and reproduction by means of four heads, even if each recording track 2 is subjected to recording and reproduction with the same apparatus, a track subjected to recording by a particular head may be subjected to reproduction by a different head. This is because the number of tracks corresponding to each repetitive recording pattern consisting of a sequence of ATF pilot signals differs from the number of heads. If recording and reproduction of the tracks are not performed by the same head, the recording and reproducing operations may become unstable due to variations in characteristics between the heads even by employing the same apparatus (self-recording and self-reproduction) which should realize recording and reproduction of optimum characteristics.
In brief, the conventional method has the following two problems: (1) the fact that if a video signal containing a very large amount of information, such as a high-definition television signal, is to be recorded and reproduced, a period of time required to introduce the tracking servo increases; and (2) the fact that, since tracks are not always subjected to recording and reproduction by the same recording/reproducing head even in the case of self-recording and self-reproduction, optimum characteristics are not obtained because of the influence of variations in the characteristics of the heads.